[Noumenon72]

You'll come back to the same pieces of code over and over, forgetting most of the details and context each time. If it takes you a while to figure out, write it down. If you had to use the debugger to find out what's in a map, leave a comment with an example of what the keys and values look like and where they're populated from.

Once you have added comments, it lets you hover over a function to remind yourself "This does X to Y when the deposit is a check", so you never have to read the internals of that function again when you're not tracing a check.

When you have to go 12 levels deep in the call stack to find the source of parameter Y, make a note in a side wiki so you can recover that detective work the next time.

Your knowledge of the code base grows like compound interest when you only have to figure out what each piece of code does once and can skip over it after that.